Well Health

Supraventricular Tachycardia Is A Condition That Can Make Your Heart Race for Hours

February 2, 2018
© Carolyn Lagattuta / Stocksy United
Quick Read

A racing heart

  • Supraventricular tachycardia (SVT) is a type of abnormal heart rhythm (also called an arrhythmia) that originates in the heart’s upper chambers, or atria, where electrical signals are received.
  • Most types of SVT aren’t dangerous on their own.
  • One type of SVT, atrial fibrillation, can be dangerous because it can lead to blood clots, which increase stroke risk.
  • Vagal maneuvers like splashing your face with cold water or coughing can slow down a rapid heartbeat.
  • Treatments like medication or catheter ablation can permanently correct SVT.

The first time my heart beat alarmingly hard and fast, I was 11 years old. I was in the middle of a dance class but knew something was wrong, so I left class and told my parents what was happening. They helped calm me down, and soon my heartbeat returned to normal.

After that first incident, the episodes kept coming, usually catching me unaware. They didn’t seem to be triggered by anything in particular: All of a sudden, my heart would start racing, making me feel tired and weak. Sometimes an episode lasted only minutes, and I could go back to what I was doing with little interruption. Other times, it lasted long enough to drain my energy, and all I wanted to do was sleep. Once, my heart raced for more than three hours.

My pediatrician referred me to a heart specialist at Seattle Children’s Hospital, who determined I had supraventricular tachycardia (SVT). SVT is an abnormal heart rhythm (also called an arrhythmia) that originates in the heart’s upper chambers, or atria, where electrical signals are received.

Normally, the sinoatrial node, a pacemaker in the right atrium, sets the heart’s rhythm. But in SVT, rapid abnormal electrical signals in the atrium overtake the sinoatrial node’s rhythm and cause the heart to race. The heart’s rapidity can mean it doesn’t pump blood effectively, causing dizziness and shortness of breath.

When the heart short-circuits

If you’ve never heard of SVT, you aren’t alone. I never had until I got it, and most people are unfamiliar with the term when I tell them about it. Yet, SVT isn’t that rare. About two in every 1,000 people have it, which translates to nearly 90,000 new cases each year. That’s more common than congenital heart defects, which are present in about 40,000 births annually.

Unlike ventricular tachycardia, which originates in the lower part of the heart (the ventricles) and leads to sudden cardiac arrest, SVT is not usually dangerous on its own. It can occur in someone who has a preexisting heart condition, but it can also occur in someone whose heart is structurally normal.

Treating patients with SVT is an everyday occurrence for Nazem Akoum, M.D., a cardiologist and director of the atrial fibrillation program at the UW Medicine Regional Heart Center.

“When I’m talking to a patient about SVT, I want to hear what they experience. Is it triggered with exercise? Does it wake them from sleep? How long do their episodes last? Their answers give me clues to what type of SVT they might have,” Akoum says. “Then, we move on to an EKG, and sometimes I ask patients to wear a heart monitor that will capture the SVT episodes.”

Atrial fibrillation and atrial flutter are both types of SVT that are more common in older patients or patients with preexisting heart conditions. Atrial fibrillation can be more serious because, for some patients, it can lead to blood clots and increase stroke risk. The other types of SVT, those that occur in people with normal hearts, commonly develop in childhood or young adulthood.

SVT in younger, healthy people is caused by an abnormal electrical pathway—a kind of short circuit—in the heart. The most common short circuit has a long name: atrioventricular node reentrant tachycardia, or AVNRT. Its name alludes to the fact that the abnormal electrical activity will form a small looping circuit involving the AV (atrioventricular) node, which transmits electrical signals from the atrium to the ventricles. As the signal races around the loop, it triggers the ventricles to fire, causing tachycardia.

The second most common type of SVT in young people, atrioventricular reentrant tachycardia (AVRT), involves an extra or accessory electrical pathway in the heart that sometimes gets activated. In this case, the signals travel through the AV node to the ventricles normally but then travel back up to the atrium via the accessory pathway, again creating a rapidly firing electrical circuit. AVRT can be a sign of a condition called Wolff-Parkinson-White syndrome, where someone is born with an accessory pathway in their heart.

For some people, SVT episodes can be triggered by caffeine, alcohol or smoking.

How to treat SVT

Atrial fibrillation and atrial flutter tend to worsen over time, but AVNRT and AVRT can behave differently. Sometimes episodes get shorter or less intense over time, which is what happened with me. Sometimes episodes stay relatively the same or get worse. And sometimes they fade entirely. Doctors don’t know why this variation occurs, Akoum says.

My episodes worsened before they let up. What started off as occasional, several-minute occurrences soon became hour-plus-long episodes that made me feel like I’d been running for hours without stopping. To help, my doctor told me there were certain things I could do—like splashing my face with icy water or doing a headstand—that might help return my heartbeat to normal. These techniques are called vagal maneuvers, because they stimulate the vagus nerve, which runs from the brain all the way down to the colon.

“Vagal maneuvers recruit the nervous system to help slow down the heart and break that short circuit,” Akoum says.

Other vagal maneuvers include coughing, gagging and holding your breath and bearing down. Not all maneuvers work for everyone. Cold water never worked for me, but headstands did.

For people whose episodes are debilitating enough to interfere with everyday life, there are solutions more lasting than vagal maneuvers. Medications designed to suppress the electrical short circuiting could be helpful for some people, Akoum says.

If a permanent fix is needed, a catheter ablation could be the solution. Akoum performs this procedure regularly. It involves the cardiologist using a thin, wire-like device threaded into the heart through a vein to locate the abnormal circuit and then destroying—or ablating—the abnormal heart tissue with heat or cold.

“If we eliminate the critical part of the circuit, which is most of the time only a few millimeters of tissue, that abnormal electrical pathway cannot be sustained anymore. That solves the problem,” Akoum says.

Ablation has a 95 percent success rate after the first try for patients with AVNRT and AVRT, Akoum says. First-attempt success is about 70 percent in patients with atrial fibrillation or atrial flutter.

The head and the heart

Though SVT isn’t typically dangerous and treatment is fairly straightforward, having any kind of heart abnormality can be anxiety-inducing. I started getting panic attacks after my first SVT episode, and often worried about what would happen if I had an episode out in public. (What happened was that I sometimes had to do vagal maneuvers in awkward places. I don’t recommend doing a headstand in a public restroom. Ew.)

Now that I’m an adult, my SVT episodes are infrequent and never last long; I might get two or three episodes each year that last for a few minutes each. But sometimes, when I’m particularly stressed out or am exercising, I worry that I’ll have another episode.

The connection between SVT and anxiety—especially in women—is not unfounded, though it is little-researched. Women who have some form of SVT may be more anxious about it, and some women with SVT are misdiagnosed as having panic disorder, in part because the symptoms of both conditions are very similar. Some researchers even speculate that panic disorder could morph into SVT, though there is currently no clear proof of this. Some types of SVT, like AVNRT, are more common in women, and atrial fibrillation may be harder to treat in women.

For me, anxiety and SVT interact. Sometimes when I’m anxious I feel like an SVT episode is about to start (usually it doesn’t). And on the rare occasion I do have an episode, I always grow tense. I try to remind myself how lucky I am that the condition improved on its own and that it probably won’t have a negative impact on my health. Even when having SVT has scared me, it’s also been a good reminder to do everything in my power—like exercising and eating well—to keep my heart healthy.